Input: synaptics-rmi4 - remove unnecessary flush_workqueue()

All work currently pending will be done first by calling destroy_workqueue,
so there is unnecessary to flush it explicitly.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: ran jianping <ran.jianping@zte.com.cn>
Link: https://lore.kernel.org/r/20220422093304.2781183-1-ran.jianping@zte.com.cn


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>